<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <script>
        function VideoCallMethod(state){
            this.state = state;
            this.$button = null;
        }
        VideoCallMethod.prototype.init = function(){
            this.$button = document.createElement('button');
            this.$button.innerHTML = '准备视频通话';
            document.body.appendChild(this.$button);
            this.eventCenter();
        }
        VideoCallMethod.prototype.eventCenter = function(){
            var that = this;
            this.$button.onclick = function(){
                that.setFn();
            }
        }
        VideoCallMethod.prototype.setFn = function(){
            if(this.state == 'ready'){
                this.$button.innerHTML = '准备视频通话';
                this.state = 'calling';
            }else if(this.state == 'calling'){
                this.$button.innerHTML = '正在视频通话';
                this.state = 'end';
            }else if(this.state == 'end'){
                this.$button.innerHTML = '视频通话结束';  
                this.state = 'ready';              
            }
        }
        
        var v1 = new VideoCallMethod('ready');
        v1.init();
    </script>
</body>
</html>